With the explosive growth of the Internet as a backdrop, wavelength division multiplexing (WDM) communication is now being transferred from the conventional point-to-point type system to the ring-mesh type system. This is because the ring-mesh type system can use a transparent wavelength selective switch or the like which processes an optical signal without changing its optical state, thereby flexibly handling variations in demand for communications between nodes. However, when optical paths are changed over in the ring-mesh type network, the dispersion values of the paths also change dynamically. This in turn requires adaptability to dispersion compensation in the optical communication path. Conventional dispersion compensators were predominantly of a type that collectively compensate a plurality of channels. However, in the ring-mesh type network which uses wavelength selective switches, optical signals of different wavelengths pass through paths of different distances. Accordingly, there was a demand to set a different dispersion value for each WDM wavelength.
For example, adaptive dispersion compensation techniques that were suggested to address such demands include those using a dispersive element and a mirror array (Patent Document 1), a waveguide (Patent Document 1 and Non-Patent Document 1), and a three-dimensional mirror and a dispersive element (Non-Patent Document 2).    Patent Document 1: Japanese Patent Laid-Open No. 2002-303805 (pp. 5-7, FIGS. 1 and 11)    Non-Patent Document 1: K. Takiguchi, K. Okamoto, and T. Goh, “Dispersion slope equalizer on planar Lightwave circuit for 40 Gbit/s based WDM transmission,” Electron. Lett, 37 (24), pp. 1-2, 2001    Non-Patent Document 2: Independent Administrative Institution-Information Communication Study Organization, “2004 Report on research and development outcomes: Research and development of high-performance integrated optical switching node for implementing economical optical networks,” 2006.
Non-Patent Document 3: X. Fan, et al., “Chirped fiber gratings characterization with phase ripples,” Proceedings of OFC2003, Vol. 2, pp. 638-640 (2003)